An assortment of Ultem/PIM-1 polymer blends was prepared and their transport properties to a series of gases were studied. Good dispersion between the PIM-1 and Ultem phases was found when the PIM-1 loading was low (<20 wt%) or high (>90 wt%). A slight shift of T-g was observed when the PIM-1 loading increased from 0 wt% to 50 wt%, suggesting likely partially miscibility. The molecular-level interactions were further confirmed by the FTIR and XRD data, where shifts of peaks were detected at several compositions. Gas transport properties of pure gases including He. N-2, O-2, CH4, CO2 for all polymer blends and mixed gases including CO2/CH4 (50/50) and CO2/N-2 (50/50) gas pairs for Ultem/PIM-1 (90:10) and Ultem/PIM-1 (80:20) blends were explored. Considerable increments in gas permeability were observed by adding only 5 or 10 wt% PIM-1 without much compromising gas pair selectivity, i.e., the CO2 permeability increased impressively over 47% and 167%, respectively, compared with the pristine Ultem. When comparing the gas permeation properties with the predictions from semi-logarithm and Maxwell equations, they follow nicely with the semi-logarithm addition when the PIM-1 loadings are low (<20 vd%), indicting relatively homogenous blends at these compositions, while the transport properties match closely with the Maxwell prediction at high PIM-1 loadings (>90 wt%) due to the good dispersion of Ultem inside PIM-1. This study opens up the potential of employing PIM-1 as an organic filler to improve the permeability of low permeable materials for other industrial membrane applications. (C) 2013 Elsevier B.V. All rights reserved.